1. Field of the Invention
This invention is directed to a process for selectively producing acetaldehyde which comprises introducing into a reaction zone (1) methanol, (2) hydrogen, (3) carbon monoxide, (4) an arsenic-cobalt tricarbonyl complex, and (5) an iodine compound and then subjecting the contents of said reaction zone to an elevated temperature and an elevated pressure for a time sufficient to convert methanol to acetaldehyde.
2. Description of the Prior Art
The synthesis of oxygenated hydrocarbons, such as aldehydes, alcohols, etc., by reacting methanol with synthesis gas (hydrogen and carbon monoxide) is not a new concept. Processes are available for producing a wide spectrum of oxygen-containing hydrocarbons, such as alcohols, aldehydes, ketones, esters, ethers and fatty acids of almost any chain length and degree of saturation. The relative amount or extent to which one or more of the above-described products is obtained is determined and/or controlled by the type catalyst used in the reaction. Catalysts which have been used in the past to produce aldehydes, alcohols, etc., are those selected from iron, cobalt, nickel, zinc and the like on a support, either alone or in combination with one or more promoter(s).
The conversion of an alcohol, for example, methanol, to an aldehyde, such as acetaldehyde, containing one carbon atom more than the original alcohol is normally a tedious and time-consuming procedure involving a series of steps. Additionally, catalysts which possess acceptable activity generally tend to give a wide spectrum of products, for example, hydrocarbons and oxygenated hydrocarbons having a broad distribution of carbon atoms. This not only complicates the separation and recovery of desired products, but results in reduced yield of said desired products and erosion of reactants in the production of undesirable products. The process herein is particularly suited to the selective formation of acetaldehyde from methanol and synthesis gas using an arsenic-cobalt tricarbonyl complex in combination with an iodine promoter.
The reaction of methanol with hydrogen and carbon monoxide to produce acetaldehyde is appreciated and disclosed by the prior art. However, most known processes produce an undesirably large mixture of alcohols, ketones and carboxylic acids in addition to the desired aldehyde.
U.S. Pat. No. 3,356,734, issued to Kurahhi et al, on Dec. 5, 1967, entitled "Process for the Production of Acetaldehyde", teaches a process for the production of acetaldehyde in two steps. In the first step, methanol, hydrogen and carbon monoxide are contacted with a cobalt catalyst and a halogen promoter to form a product predominating in acetals. The cobalt catalyst described is selected from cobalt salts which are soluble in methanol. In particular, preferred soluble salts include cobalt acetate, cobalt bromide, chlorate, chloride, iodide, sulfide and the like. The halogen promoter is selected from iodine, bromine, chlorine and the like. In the second step, the acetals so produced are contacted with a second distinct catalyst system to hydrolyze the acetals to acetaldehyde and methanol. Maximum possible selectivity to acetaldehyde is from about 17 to about 38 mol percent of the converted methanol.
Another process for producing aldehydes is disclosed in U.S. Pat. No. 3,996,288, entitled "Method of Producing Aldehydes by Hydroformylation"; issued to Yukata et al, on Dec. 7, 1976. Particularly, the reference relates to a process for preparing phenylacetaldehyde by contacting hydrogen, carbon monoxide, an amide of a carboxylic acid and benzyl chloride at elevated temperature and pressure in the presence of a carbonylation catalyst, for example, dicobalt octacarbonyl. The reference, however, fails to appreciate a process for the selective formation of acetaldehyde from methanol, hydrogen and carbon monoxide.